Centrifuge test tube cap



Aug. 5, 1969 c. MARKS CENTRIFUGE TEST TUBE CAP F'il d Sept. 16, 1965 l E m M 5 LLOYD c. MARKS INVENTOR. BY 5 l ATTORNEY fig. 5

United States Patent 3,459,369 CENTRIFUGE TEST TUBE CAP Lloyd C. Marks, Saratoga, Calif., assignor to Beckman Instruments, Inc., a corporation of California Filed Sept. 16, 1965, Ser. No. 487,770 Int. Cl. B04b 7/00 US. Cl. 23326 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to centrifuges in which the material to be centrifuged is placed in test tubes carried by the centrifuge rotor. More particularly, the present invention relates to the caps which are used to seal the tops of the test tubes.

Analytical and preparative centrifuges are commonly provided with a rotor having a series of cavities, usually arranged in circular fashion, adapted to receive test tubes for carrying the sample to be centrifuged. In the typical analytical or preparative centrifuge rotor, the axis of each cavity is angularly oriented with respect to the vertical rotational axis of the rotor so that the bottom of the test tube is further from the rotor axis than the top. Inclined-tube rotors are advantageous in that initially, precipitate is collected at the bottom of the tube at a more rapid rate than if a tube having its longitudinal axis perpendicular to the rotor axis were used. During rotor operation, the sample is caused to climb up the centrifugal (outermost) side of the tube wall. Eventually, when a sufficiently high rotational speed is reached,'the surface of the sample stands almost parallel with the rotor axis To prevent leakage of the sample, each test tube is pro' vided with a cap sealing off the mouth. It will be evident that if the test tube used in an angle rotor is initially full or almost full, leakage of the sample from the top of the test tube will occur unless the cap provides an adequate seal.

In accordance with one form of centrifuge test tube cap of the prior art, a stem, a mating crown and a flat, resilient washer, interposed between the stem and crown, are utilized. The stem is situated inside the upper part, or mouth, of the test tube and the crown is dimensioned to fit snugly over the mouth. The stem and crown are coaxially coupled by suitable fastening means usually in the form of a crown-engaging nut threaded on a stud projecting from the stem. The stem has an upper, horizontal surface and the crown a lower horizontal surface. The resilient washer is disposed between these surfaces and compressed when the fastening nut is secured. Compression deforms the washer causing it to sealingly engage both the inner wall of the test tube and the stud projecting from the stem.

A problem connected with the use of the test tube caps of the prior art is that they often leak when the tubes are subjected to high centrifugal forces. Leakage appears to be caused by distortion or cold flow of the resilient gasket outwardly in the centrifugal field. Torquing down the cap nut more tightly does not always prevent cold flow. Moreover, the level of torque that is necessary to effect an adequate seal may be relatively high. Cold flow of the gasket can also lead to its failure, making removal of the cap difiicult and re-use of the gasket impractical.

Accordingly, it is an overall object of the present invention to provide a leakproof test tube cap which may be utilized with a substantially full test tube carried by an angle centrifuge rotor.

It is a more specific object of the present invention to provide a leakproof centrifuge test tube cap in which cold flow of the resilient gasket element is substantially eliminated.

It is a further object of the present invention to provide a centrifuge test tube cap requiring a relatively small tightening force to effect a substantially leakproof seal.

According to one specific, exemplary form or embodiment of the present invention shown and described herein, there is provided a test tube cap comprising generally a stem provided with an outwardly sloping surface, a crown also having an outwardly sloping surface and a gasket disposed between the sloping surfaces. Fastening or clamping means are provided whereby the stem and crown may be clamped together. The outside surface of the stem is dimensioned for a snug fit With the inside wall surface of the test tube. The crown has an inwardly-facing surface dimensioned for a snug fit with the outside surface of the test tube. With the stem, crown and resilient gasket in place on the test tube, tightening of the clamping means causes the gasket to be compressed between the outwardly sloping surfaces of the crown and stem and simultaneously wedged against the inside wall surface of the test tube. As a result of this action the outside surface of the tube is pressed against the inwardly-facing surface of the crown. With the gasket closely confined in the space defined by the outwardly-sloping surfaces and the inside surface of the test tube wall, cold flow of the gasket, when the assembly is subjected to high centrifugal forces, is substantially eliminated. In addition, the wedging action, which biases the gasket against the inside test tube wall and, in turn, the outside surface of the test tube against the inwardly-facing surface of the crown, creates a uniform and substantially leakproof seal. An important advantage of the cap of the present invention is that only a relatively small clamping force is necessary to achieve a leakproof seal.

To minimize relative lateral motion between the crown and the stern, and thereby further prevent cold flow of the resilient gasket, another aspect of the present invention provides for peripheral clearance between the crown and the upper part of the rotor cavity receiving the test tube. Relative lateral motion between the crown and stem is further prevented by providing the stem and crown with mating surfaces which interlock when these parts are brought together.

The novel features which are believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof can best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a perspective, exploded view of a test tube cap illustrative of the present invention;

FIG. 2 is a top view of an assembled test tube cap in accordance with the present invention;

FIG. 3 is a sectional side view of the cap assembly of FIG. 2 taken along the plane 3-3;

FIG. 4 is a sectional side view of a crown element in accordance with the present invention; and

FIG. 5 is a sectional side view of a stem element in accordance with the present invention.

Turning now to the drawings, there is shown a centrifuge test tube cap comprising generally a crown 10, a stem 40, a resilient gasket in the form of an O-ring 60, a nut 70, an insert 80 and a setscrew 90.

The crown 10, the details of which are best shown in FIG. 4, has generally a cylindrical shape and is provided with a depending skirt 12 and a depending step 14 positioned interiorly of, and concentrically with, the skirt 12. The skirt 12 has an exterior, cylindrical surface 16, an inwardly-facing surface 17 dimensioned for a snug fit with the outside wall surface of the test tube and a lower seating surface 18. The depending skirt 12 and the depending step 14 define between them an annular groove 20 for receiving the mouth of the test tube as shown in FIG. 3. The depending step 14 includes an outwardly sloping surface 22 and an inner vertical surface 24. The crown is further provided with a centrally-located hole 26 and a circular recess 28 positioned coaxially with the hole 26.

The stem 40, shown in detail in FIG. 5, has a downwardly-extending cylindrical wall 41 with an outside surface 42 dimensioned to fit snugly inside the upper portion of the test tube as shown in FIG. 3. An axial, threaded stud 44, having a center hole 46, projects upwardly from an upper, horizontal surface 48. The stem 40 is further provided with a peripheral step 50 defined by a vertical surface 52 and an outwardly-sloping surface 54. The corner of the peripheral step 50 may be filleted as shown at 56. A hole 56 in the wall 41 aids in breaking the seal which may exist between the stem 40 and the test tube when the cap is removed.

FIG. 3 shows the assembled cap in place over the mouth of a centrifuge test tube. The stud 44 projects through the hole 26 in the crown and receives the nut 70. The outwardly sloping surfaces 22 and 54 on the crown and the stem, the inside wall surface of the test tube and the vertical surface 52 of the peripheral step 50 together form a chamber having a generally trapezoidal cross-sectional shape. The O-ring 60 is confined within this chamber. As the nut 70 is tightened, the O-ring 60 is compressed and deformed, the sloping surfaces 22 and 54 wedging the O-ring outwardly against the inner wall surface of the test tube. This action in turn biases the outside wall surface of the test tube against the surface 17 of the skirt 12. Because of the wedging action provided by the sloping surfaces and because of the relatively small surface area of the O-ring, only a small torque need be applied to the nut 70 to effect an adequate seal even under high centrifugal forces.

The center hole 46 in the crown 40 permits the removal of the tube contents with an instrument such as a hypodermic syringe. During centrifugation, the center hole is closed off by means of a threaded insert 80. A setscrew 90 may be used to lock the insert 80 in place.

To prevent cold flow of the O-ring 60, and to prevent leakage caused by distortion of the mouth of the test tube during high rotational speeds, it is most important that relative lateral motion between the crown 10 and the stem 40 be kept to a minimum. A first structural aspect for accomplishing this is the interlocking feature provided by the surfaces 24 and 52 on the crown and the stem, respectively. It may be seen in FIG. 3 that these surfaces engage in a sliding fit when the step and crown are joined. A second feature for accomplishing this is also shown in FIG. 3. It may be seen that the centrifuge rotor, shown in phantom, is provided with a cavity having a lower portion 100 for receiving the test tube in a close fit and an upper recess 102. A horizontal surface or seat 104 forms the lower extremity of the recess 102. With the capped test tube in place, the lower surface 18 of the crown 10 bears against the seat 104. A small amount of clearance, designated by the letter A in FIG. 3, is provided between the outer surface 16 of the crown and the recess 102. In other words the diameter of the recess 102 is sutliciently greater than the diameter of the crown 10 to form a peripheral clearance A between the crown and the recess. The clearance A assures that if there is any lateral movement of the test tube and stem when subjected to high centrifugal forces, the crown will move with the stem. The confining space or chamber containing the O-ring 60 will therefore remain uniform in cross section around the entire periphery of the cap.

It will be obvious to those skilled in the art that various modifications may be made to the specific exemplary embodiments of the invention described. While particular embodiments have been discussed, it will be understood that the invention is not limited thereto and that it is contemplated to cover in the appended claims any such modifications as fall within the true spirit and scope of the invention.

, What is claimed is:

1. A centrifuge test tube cap for a test tube comprising:

a stem, including an outside surface dimensioned for a snug fit with the inside wall surface of said test tube and having a sloping surface extending outwardly in a downward direction toward the outside surface;

a crown, having an inwardly-facing surface dimensioned for a snug fit with the outside wall surface of said test tube and having a sloping surface extending outwardly in an upward direction toward the inwardly-facing surface;

means for clamping together said stem and said crown;

and

a resilient gasket disposed between said outwardly sloping surfaces of said stem and said crown, whereby, as said stem and said crown are clamped together, said gasket is compressed and wedged against the inside wall surface of said test tube, said outside wall surface of said test tube being biased against said inwardly-facing surface of said crown.

2. A test tube cap, as defined in claim 1, in which said means for clamping said stem and said crown together comprises:

a stud extending upwardly from said stem;

2. hole in said crown for receiving said stud; and

a nut threaded on said stud.

3. A centrifuge test tube cap for a test tube comprising:

a stem including an upper surface and an outside surface dimensioned for a snug fit with the inside wall surface of said test tube, a stud projecting upwardly from the upper surface of the stern and a peripheral step joining said upper surface with said outside surface of the stem, said peripheral step including a sloping surface extending outwardly in a downward direction toward the outside surface;

a crown, mounted on said stud, including a depending skirt having an inwardly-facing surface dimensioned for a snug fit with the outside wall surface of said test tube and having a depending flange, said skirt and said flange defining a groove for receiving the mouth of said test tube, said flange having a lower, sloping surface extending outwardly in an upward direction whereby a substantially trapeZoidally-shaped chamber is formed with said peripheral step and said inside wall surface of said test tube;

an O-ring disposed in said trapezoidally-shaped chamber; and

a nut threaded on said stud, whereby, as said nut is tightened, said O-ring is compressed between said outwardly sloping surfaces of said stem and said crown and wedged against said inside wall surface of said test tube, said outside wall surface of said test tube being thereby biased against said inwardly-facing surface of said skirt.

4. A test tube cap, as defined in claim 3, in which said peripheral step of said stem and said depending flange of said crown mate as said nut is tightened thereby substantially preventing lateral relative motion between said stem and said crown.

5 6 5. A combination comprising a centrifuge rotor, a test said crown and said stem shift substantailly as one tube and a test tube cap closing off the mouth of said unit when said combination is subjected to high test tube, said cap including a crown and a mating stem, centrifugal forces. said crown positioned over said mouth of said test tube References Cited and having a lower surface, said centrifuge rotor having a cavity for receiving said test tube and said test tube cap, 5 UNITED STATES PATENTS in which 2,831,714 4/ 1958 Thorburn 2771 17 XR said cavity includes a lower portion for receiving said 3,071,316 1/1963 P m n e et a1. 23292 XR test tube in a snug fit and an upper recess for re- 3,265,296 8/1966 Mitchell 23326 ceiving said crown, said recess having a seat against 10 MORRIS WOLK, Primary Examiner 'WhlCll said lower surface of said crown bears, the d1- I ameter of said upper recess being sufiiciently greater REESE Asslstant Exammer than the diameter of said crown to form a peripheral s CL clearance between said crown and recess whereby 23 292; 277 115 

